1. Field of the Invention
This invention pertains generally to wells for production of petroleum products from subsurface earth formations and more particularly concerns completion systems for wells, including formation fracturing and other treatment for enhancement of well production. Even more specifically, the present invention concerns a method and apparatus for cleaning a fractured or otherwise treated perforated casing interval between spaced packers to permit repositioning or removal of the apparatus.
2. Description of Related Art
When a fracturing treatment is performed on a zone isolated by packers, two problems are prevalent: 1) erosion of the tool and casing due to high velocity flow of abrasive fluids, and 2) cleanup of slurry/proppant in the annular area between the casing and the isolation tool. This invention addresses both of these issues.
Conventional coiled tubing conveyed fracturing tools have spaced packer elements, such as cup packers, and typically provide a fracturing port or ports located just uphole from the lower packer element and a dump port (if used) that is located below the lower packer element. This arrangement works well when clean fluid is reverse circulated down the annulus and up the coiled tubing to clean underflushed slurry that is typically present in the coiled tubing and in the fracturing tool after fracturing a zone. The reverse circulated clean fluid flows over the upper packer, down the casing-tool annulus between the packers, into the tool via the fracturing port, and up the coiled tubing to the surface. By locating the fracturing port near the lower packer element, cleaning of the straddle interval between the packers is optimized.
On some jobs a fracturing tool is provided with a dump port, and clean flushing fluid is pumped down the coiled tubing to displace the underflushed slurry in the coiled tubing to the wellbore below the tool. According to this arrangement, which employs no reverse circulation, the slurry remaining in the annulus interval between the packers may not be effectively cleaned.